The present invention relates generally to welding equipment and more particularly to systems and methods for selective application of power to an electrical device associated with a welding operation.
Electric welders and associated electrical apparatus are employed in a variety of field applications, in which electric power is applied between a workpiece to be welded and a filler material, such as welding wire, which operates as a consumable electrode. For instance, in many conventional welding systems, a controlled DC voltage of between 20 and 100 volts is applied to the welding wire while the workpiece is connected to a power supply common. The application of such power is controlled so as to melt the welding wire to provide molten filler material to a weld joint in a controlled fashion. Welders commonly include an electric power supply which operates to control a voltage potential between the workpiece and a metal welding wire being fed to the weld joint at a controlled feed rate or speed, wherein a wire feeder controls the wire feed rate. Often, the wire feeder includes a metal roll cage contacting the workpiece, which may serve as a common return conductor path to the workpiece, as well as providing a carrying handle for transport of the wire feeder. The welder and associated power supply are sometimes located remotely from the weld station and the workpiece, whereas the wire feeder is typically located proximate the weld station. The wire feeder typically includes electrically powered (e.g., automatic or semi-automatic) wire feed mechanisms, such as one or more pairs of motor driven feed rollers which advance the weld wire to the weld operation.
In a common situation, the wire feeder receives electrical power for operation of such wire feed mechanisms from the welder power supply. In this configuration, a first voltage potential is connected to the wire feeder via the weld wire. The wire feeder chassis may serve as a common return path, for instance, wherein the wire feeder is supported on large metal structures being welded. Alternatively, an electrical return path is sometimes provided from the wire feeder to a grounded workpiece through a grounding device, such as a grounding clamp type connector. Where the wire feeder includes a metal roll cage, the ground clamp may be secured to the roll cage in order to provide the return path via the workpiece. Thus, for example, an operator may manually connect a ground clamp to the roll cage or to the workpiece as it enters the weld station, thereby establishing a low impedance return path for the powered wire feeder. In this instance, the wire feeder chassis may be electrically isolated from the electrical system, and the manually operated ground clamp may include insulated hand grip areas. In addition to wire feeders, other electrical devices associated with a weld operation may similarly receive operational power from the welder power supply, wherein a return path may be provided to the power supply common via a ground clamp or other grounding device, or alternatively via the chassis.
Whether the common return path is provided through a grounding device, or through the wire feeder chassis, it is desirable to ensure a proper, low impedance, return path connection prior to operation of the wire feeder or other electrical devices associated with the welding operation. In situations where multiple workpieces are welded at a welding station, the operator must secure the ground clamp from the wire feeder device to each workpiece prior to beginning the weld operation. Where the wire feeder chassis serves as the common return path, it is necessary to ensure connection of the chassis to the grounded workpiece. In addition, where a wire feeder with a metal roll cage is transported to a new welding site, the ground clamp must be secured to the roll cage prior to beginning operation. Although not recommended, the welder power supply is often left energized while finished workpieces are replaced with new ones, during which time the return path (e.g., through the device chassis or ground clamp) is interrupted. Similarly, where the wire feeder or other electrical device is transported, the common return path may be improperly re-established. Improper re-establishment of the return path may occur, for example, where a ground clamp is connected to the power supply common through a finite intermediate impedance, whereupon operation of the electrical device may cause stress or damage to the device. Thus, there is a need for systems and methods for selective application of power to an electrical device associated with a welding operation, for example, by which the propriety of a device return path connection is ensured prior to operation thereof.
The following presents a simplified summary of the invention in order to provide a basic understanding of one or more aspects thereof. This summary is not an extensive overview of the invention, and is intended neither to identify key or critical elements of the invention, nor to delineate the scope of the invention. Its primary purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention is directed to systems and methods for determining or sensing an impedance between a grounding device and an electrical device related to a welding operation, and for controlling current flow through the electrical device according to the sensed impedance. The invention may be employed for ensuring proper ground connection of the electrical device prior to allowing current flow therethrough by discriminating between proper ground or return path connections and improper connections. For example, the invention may be advantageously employed to determine whether a welding wire feeder common terminal is properly secured to a welder power supply common before allowing current to flow through the wire feeder. This provides significant advantages in applications in which the wire feeder common connection is established using a ground clamp grounding device or the like, wherein an operator secures the ground clamp terminals to a grounded workpiece prior to performing a welding operation thereon.
One aspect of the invention provides a discriminator system for selectively allowing current to flow through an electrical device associated with a weld operation. The system, which may be employed in association with a wire feeder or other device, includes a first switch component, such as a transistor, relay, or the like, connected between a common or ground terminal of the electrical device and a grounding device, such as a wire feeder ground clamp or the like, to selectively provide electrical connection therebetween according to a first control signal. A sensor is provided to sense an impedance between the grounding device and a power supply common, and to provide the control signal to the switch component according to the impedance. The system can thus distinguish between appropriate (e.g., low impedance) common connections, and other inappropriate impedances, for example; such as by determining whether the sensed impedance exceeds a threshold. In one implementation, the control signal can comprise a first state allowing current flow through the device when the impedance is less than the threshold, a second state preventing or inhibiting current flow when the impedance is greater than the threshold.
The sensor may comprise a sense resistor with one terminal connected to one of a power supply voltage and the grounding device, and a second switch selectively connecting the other sense resistor terminal to the other of the power supply voltage and the grounding device according to a second control signal. A sensor circuit senses the voltage across the sense resistor and provides the first control signal to the first switch in accordance therewith. The connection of the sense resistor between the power supply voltage and the grounding device may be intermittent, such as using pulse width modulation, to limit the amount of average current flow through the grounding device in case of improper grounding thereof. Thus, although a sense current is used to measure the impedance between the grounding device and the power supply common, the sense current may be controlled so as to prevent adverse effects while obtaining the impedance value. In this regard, the sense resistor may be advantageously sized so as to limit the sense current to a predetermined value. Furthermore, the sense resistor size may be adjusted so as to provide for determination of a specific range of impedances of interest between the grounding device and the power supply common. In this manner, an impedance below a certain threshold value may be determined to be proper, whereas a higher return path impedance is detected and used to inhibit current flow through the electrical device, by which protection of the device may be facilitated.
Another aspect of the present invention provides methodologies for selectively allowing current to flow through an electrical device, wherein an impedance between a grounding device and a power supply common is sensed and the device is selectively connected to the grounding device according to the sensed impedance. For example, in order to prevent or inhibit device current flow where an improper common return connection exists, the electrical device may be connected to the grounding device (e.g., to thereby establish a conductive return path) if the sensed impedance is less than a threshold value and disconnected therefrom if the impedance is greater than the threshold value. Sensing the impedance may be accomplished in any appropriate manner. For example, a sense resistor may be connected between a power supply voltage terminal and the grounding device, and a voltage across the sense resistor may be ascertained. The sense resistor may be intermittently switched, such as through pulse width modulation applied to a transistor or relay type switching device, whereby the resulting sense current may be limited to a predetermined value.
Yet another aspect of the invention provides systems for determining an impedance between a grounding clamp and a power supply common. A sense resistor is provided in the system, having a first terminal in electrical communication with one of a power supply voltage terminal and the grounding device, along with a switching device operative to selectively connect a second terminal of the sense resistor to the other of the power supply voltage terminal and the grounding device. The system further comprises a sensor circuit operative to sense a voltage across the sense resistor and to provide a signal indicative of the impedance between the grounding clamp and the power supply common according to the voltage across the sense resistor.